The present relates to inhibition of delivery of inappropriate controlling currents to a heart.
The application of a non-excitatory field to the heart, in order to modify its contractility and/or have another desirable controlling effect on the heart is described, for example in PCT/IL97/00012, the disclosure of which is incorporated herein by reference.
Such non-excitatory signals can cause, in some cases, an arrhythmia, which may be potentially fatal, for example if it is applied to excitable tissue. The signal is applied, in some devices, in a time window determined based on a locally sensed depolarization event. Such a window will also tend to prevent pro-arrhythmia effects, at least in some cases. However, if an arrhythmia exists, the applied non-excitatory signal can cause a further arrhythmia.
However, in spite of these and other safety measures that may be applied, there remains the danger that an applied non-excitatory signal will inadvertently cause or interact with an arrhythmia.
An aspect of some embodiments of the invention relates to using a wide-field ECG signal to determine when to inhibit the application of a non-excitatory control signal (ETC). The application of an ETC signal may be prevented or an ETC signal being applied may be stopped and/or modified. In an exemplary embodiment of the invention, the ETC signal is designed to increase contractility, decrease contractility, change an activation profile (e.g., conduction velocity or heart rate) and/or prevent propagation of arrhythmia.
In an exemplary embodiment of the invention, the wide-field ECG signal contains contributions from a significant portion of the heart and is used to determine if the heart, as a whole (or a significant portion thereof) is experiencing a normal activation profile (e.g., one for which the ETC signal is suitable). In an exemplary embodiment of the invention, the wide-field ECG includes contributions from two or more chambers and/or from a heart portion having a surface area of over 3, 5 or 15 cm2.
In an exemplary embodiment of the invention, the wide-field ECG is compared to one or more templates of suitable or unsuitable heart ECGs. In an exemplary embodiment of the invention, the ECG comprises a trace of the ECG from the start of the beat until when the ETC signal is applied. Alternatively other methods of matching an ECG signal to stored signal parameters are used.
An aspect of some embodiments of the invention relates to a method of acquiring and/or maintaining a xe2x80x9cnormalxe2x80x9d template of heart ECG activation In an exemplary embodiment of the invention, a plurality of ECG traces are accumulated for heart cycles. The ECG traces may be accumulated separately for different states, for example, for machine-paced cycles and for autonomous-paced cycles. In an exemplary embodiment of the invention, a dispersion (and/or other variation-related parameter) of the ECG traces is calculated. Possibly, the dispersion is used when matching an ECG trace to the template, to determine if the trace xe2x80x9cfitsxe2x80x9d the template or not.
In an exemplary embodiment of the invention, the template is continuously updated, possibly also with xe2x80x9cabnormalxe2x80x9d ECG traces. In an exemplary embodiment of the invention, this type of updating allows the template to track changes in the normal activation of the heart.
Alternatively or additionally, when a template is not matched for a considerable period of time (e.g. 120 beats), it is dropped. Revival may be automatic, for example if the template matches at least a threshold amount over a threshold period. Alternatively or additionally, revival may be manual, for example, by a physician that programs an ETC controller that delivers the non-excitatory signal.
There is thus provided in accordance with an exemplary embodiment of the invention, apparatus for applying a non-excitatory signal to a heart, comprising:
at least one electrode;
a power source;
a wide-field ECG sensor that receives a wide-field ECG signal containing contributions from non-local sized portions of the heart;
a controller for selectively electrifying said at least one electrode with a non-excitatory signal from said power source; and
a safety filter that inhibits said electrifying responsive to said wide-field ECG signal. Optionally, said wide-field ECG sensor detects electric field contributions from at least two heart chambers. Alternatively or additionally, said wide-field ECG detects electric field contributions from an area of at least 5 cm2 of the heart. Alternatively or additionally, said wide-field ECG detect electric field contribution from all area of at least 15 cm2 of the heart.
In an exemplary embodiment of the invention, said wide-field ECG sensor detects electric field contributions from at least one quarter of a heart chamber. Alternatively or additionally, said wide-field ECG sensor detects electric field contributions from at least one third of a heart chamber.
In an exemplary embodiment of the invention, said wide-field ECG sensor detects electric field contributions from parts of the heart that are expected to be activated prior to said electrifying. Alternatively or additionally, said wide-field ECG sensor detects electric field contributions from parts of the heart that are expected to be activated after to said electrifying. Alternatively or additionally, said wide-field ECG sensor includes at least one component shared with a sensor used for timing said electrifying. Optionally, said wide-field ECG sensor shares said at least one electrode.
In an exemplary embodiment of the invention, said non-excitatory signal increases a contractility of at least a portion of said heart.
In an exemplary embodiment of the invention, said safety filter includes a template matcher that matches said ECG trace to at least one template. Optionally, said template matcher matches said ECG trace to at least one template suitable for a paced heart and at least one template suitable for an unpaced heart. Alternatively or additionally, said at least one template includes at least two templates, each designated for different heart rates. Alternatively, said at least one template includes a single template suitable for multiple heart rates.
In an exemplary embodiment of the invention, said at least one template includes at least two templates, each designated for a different non-excitatory signal. Alternatively or additionally, said at least one template includes at least two templates, each designated for a wide-field ECG sensing area. Alternatively or additionally, said at least one template includes an ECG portion corresponding to a period between a right ventricle pacing or sensing event and a time for application of a non-excitatory signal. Alternatively or additionally, said at least one template is continuously updated. Optionally, said at least one template is updated to be a weighted average of a current template and a current ECG signal. Alternatively, said at least one template is updated with both normal and abnormal ECG signals.
In an exemplary embodiment of the invention, said filter ignores templates that did not match for a considerable period of time. Alternatively or additionally, said filter prevents said electrification from starting.
In an exemplary embodiment of the invention, said filter stops an ongoing electrification from continuing. Alternatively or additionally, said filter is configured to prevent arrhythmia to be caused by said non-excitatory signal. Alternatively or additionally, said filter is configured to prevent inefficient non-excitatory signal to be applied to said heart.
In an exemplary embodiment of the invention, said wide-field ECG sensor comprises two electrode portions spaced apart at least 3 centimeters. Optionally, said wide-field ECG sensor comprises two electrode portions spaced apart at least 5 centimeters. Alternatively or additionally, at least one of said two electrode portions is adapted to be placed distanced from the heart. Alternatively or additionally, at least one of said two electrode portions is adapted to be in contact with the heart""s inner surface. Alternatively or additionally, at least one of said two electrode portions is adapted to be in contact with the heart""s outer surface. Alternatively or additionally, at least one of said two electrode portions is adapted to float in the heart""s volume. Alternatively or additionally, said two electrodes are mounted on a same elongate lead.
There is also provided in accordance with an exemplary embodiment of the invention, a method of determining if to inhibit the application of a non-excitatory signal to the heart, comprising:
detecting a non-local ECG trace;
determining if said trace indicates a normal activation of the heart; and
inhibiting the application of a non-excitatory signal responsive to a negative determination of said trace.